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4 Overview In Chapter 9, our goals are for the students to: 1. Understand the molecular and mass information given in a balanced equation. 2. Learn to use a balanced equation to determine the relationships between moles of reactants and moles of products. 3. Learn to relate masses of reactants and products in a chemical reaction. 4. Learn to recognize the limiting reactant in a reaction. 5. Learn to use the limiting reactant to do stoichiometric calculations. 6. Learn to calculate actual yield as a percentage of theoretical yield.

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7 Information Given by the Chemical Equation The coefficients in the balanced chemical equation shows the molecules and mole ratio of the reactants and products Since moles can be converted to masses, we can determine the mass ratio of the reactants and products as well

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9 Fundamentals of Stoichiometry 1.Stoichiometry is the quantitative study of reactants and products in a chemical reaction. The quantitative relationships in a given chemical reaction can be obtained from a balanced chemical equation. 2.The key concept is the use of the coefficients in the balanced chemical equation to establish mole ratios of the various materials (reactants and products) involved in the reaction. 3.The mass of the various materials can then be obtained from the molar mass ratios.

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17 ¯Use the molar mass of the given quantity to convert it to moles °Use the mole relationship to convert the moles of the given quantity to the moles of the desired quantity Example #2 Determine the Number of grams of Carbon Monoxide required to react with 48.0 g Oxygen, and determine the mass of Carbon Dioxide produced

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18 ±Use the molar mass of the desired quantity to convert the moles to mass Example #2 Determine the Number of grams of Carbon Monoxide required to react with 48.0 g Oxygen, and determine the mass of Carbon Dioxide produced

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19 Limiting and Excess Reactants A reactant which is completely consumed when a reaction is run to completion is called a limiting reactant A reactant which is not completely consumed in a reaction is called an excess reactant –calculate the amount of excess reactant unused by (1) calculating the amount of excess reactant used from the limiting reactant, then (2) subtract this amount from the amount of excess reactant started with –The maximum amount of a product that can be made when the limiting reactant is completely consumed is called the theoretical yield

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20 Limiting Reactant The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed. Fig. 4.4 The molecular state picture of the reaction of 6 molecules each of H 2 and O 2 illustrating that H 2 is the limiting reactant (L.R.).

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23 ®Use dimensional analysis to determine the number of moles of reactant A needed to react with reactant B Example #3 Determine the Number of Moles of Carbon Dioxide produced when 3.2 moles Oxygen reacts with 4.0 moles of Carbon Monoxide

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24 ¯Compare the calculated number of moles of reactant A to the number of moles given of reactant A –If the calculated moles is greater, then A is the Limiting Reactant; if the calculated moles is less, then A is the Excess Reactant –the calculated moles of CO (6.4 moles) is greater than the given 4.0 moles, therefore CO is the limiting reactant Example #3 Determine the Number of Moles of Carbon Dioxide produced when 3.2 moles Oxygen reacts with 4.0 moles of Carbon Monoxide

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25 °Use the limiting reactant to determine the moles of product Example #3 Determine the Number of Moles of Carbon Dioxide produced when 3.2 moles Oxygen reacts with 4.0 moles of Carbon Monoxide

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27 ¯Determine the moles of each reactant Example #4 Determine the Mass of Carbon Dioxide produced when 48.0 g of Oxygen reacts with 56.0 g of Carbon Monoxide

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28 °Determine the number of moles of reactant A needed to react with reactant B Example #4 Determine the Mass of Carbon Dioxide produced when 48.0 g of Oxygen reacts with 56.0 g of Carbon Monoxide

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29 ±Compare the calculated number of moles of reactant A to the number of moles given of reactant A –If the calculated moles is greater, then A is the Limiting Reactant; if the calculated moles is less, then A is the Excess Reactant –the calculated moles of O 2 (1.00 moles) is less than the given 1.50 moles, therefore O 2 is the excess reactant Example #4 Determine the Mass of Carbon Dioxide produced when 48.0 g of Oxygen reacts with 56.0 g of Carbon Monoxide

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30 ²Use the limiting reactant to determine the moles of product, then the mass of product Example #4 Determine the Mass of Carbon Dioxide produced when 48.0 g of Oxygen reacts with 56.0 g of Carbon Monoxide

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31 ³Divide the actual yield by the theoretical yield, then multiply by 100% The actual yield of CO 2 is 72.0 g The theoretical yield of CO 2 is 88.0g Example #4a Determine the Mass of Carbon Dioxide produced when 48.0 g of Oxygen reacts with 56.0 g of Carbon Monoxide If 72.0 g of Carbon Dioxide is actually made, what is the Percentage Yield

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34 Percent Yield Most reactions do not go to completion The amount of product made in an experiment is called the actual yield The percentage of the theoretical yield that is actually made is called the percent yield Percent Yield = Actual Yield Theoretical Yield x 100%

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40 Theoretical Yield is the amount of product that would result if all the limiting reagent reacted. Its amount is Calculated using the balanced equation. Actual Yield is the amount of product actually obtained from a reaction. It is usually given.